In the field of x-ray and gamma-ray detection and imaging, it is known that lens structures are ineffective for focusing highly energetic photons. As a result, when detection or imaging of an X-ray or gamma-ray source is desired, other techniques must be used to scale the target emissions to an appropriate detector. For example, a pinhole collimator may be used to constrain energetic photons of the target to an image detector. In such configurations, a small hole is drilled through a high-Z material. The pinhole collimator is disposed between the target and the detector at a suitable distance from the detector. Emissions from the target pass through the penetration in the pinhole collimator, and an inverted image of the target is exposed upon detector. It is noted that decreasing the pinhole diameter yields increased spatial resolution. However, since fewer photons reach the detector in a given time, as the pinhole aperture becomes smaller additional exposure time is required to obtain an acceptable image from a given intensity target.
To overcome this limitation, it is possible to use a plurality of pinholes disposed in a high-Z material as noted above. This may be referred to as a coded aperture mask. This increase in pinhole aperture area yields a proportional increase in the number of photons received by the detector in a given period of time. Therefore the exposure duration may be reduced for a given target in this configuration. However, the coded aperture necessarily projects a plurality of overlapping images onto the detector. Computer executed algorithms may be performed to unify the plurality of projected images captured by the detector. Unfortunately, inherent noise associated with the plurality of pinholes' placement, and transient signals from the detector, tend to produce unacceptable amounts of distortion and blur.
It has been observed that imaging the same target with a variety of physically different masks, or apparently different (presented to the target and detector in a different orientation) masks, allows effective noise reducing techniques to be employed. When a given target is imaged with a plurality of different coded apertures, the data corresponding to the target will be readily identifiable, while the data corresponding to inherent noise will change from mask configuration exposure to a different mask configuration exposure. Such noise may then be effectively identified and excluded.
Some systems use a plurality of tungsten or lead plates that are selectively interchanged for each imaged exposure. Other systems translate or rotate the mask with respect to the image and detector. However, each of those techniques yields a relatively small number of distinct patterns. Moreover, the pre-established patterns may not be readily reconfigured to assist in the imaging under particular environmental and target orientation conditions.
Despite the current advances in X-ray and gamma-ray imaging systems and techniques, there remains a need for apparatus and methods of improved imaging of a radioactive target with a fully reconfigurable coded aperture mask, buy use of a reconfigurable liquid attenuated collimator apparatus.